This invention relates to an endoscope apparatus with an insertion part having a small outer diameter which includes an object optical system to conduct measurements or stereoscopic-vision observations.
Conventionally, an endoscope which includes a long and thin insertion part which is inserted into a cavity or the intra-corporeal of a human being for observation, etc., has been widely used in both the industrial field and the medical field. Furthermore in recent years, there have been a great need to measure the size and the depth of flaws and cracks in the industrial field, and to perform surgery using an endoscope in the medical field. Moreover in the medical field, using stereo images to recognize depth information is well known.
A conventional endoscope in which stereo observation are possible is described in Japanese Laid-open Patent Publication No. 8-29701. As shown in FIG. 6, two objective-lens systems are arranged in parallel and at the end of an endoscope insertion part. The endoscope conducts parallax stereoscopic vision by receiving an image from two image-pick-up devices (henceforth, CCD) and shifting the image due to the positional differences of the two CCDs.
In the optical system with two CCDs, since the number of pixels can be increased as compared to one CCD, it is effective in improving the image quality of stereo images and the precision of measurements. However, by arranging two CCDs in parallel, it then becomes difficult to reduce the size of an endoscope which makes it difficult to observe a narrow site or perform minimum invasive surgery.
A conventional endoscope having an optical system in which an image with a parallax is formed on one CCD is described in Japanese Laid-open Patent Publication No. 7-35989. As shown in FIG. 7, this optical system has one CCD on the extension line of the respective optical axis of the two object optical systems arranged in parallel to form two images. The distance between the two optical axes is hereinafter referred to as xe2x80x9cthe optic-axial distancexe2x80x9d.
On the one hand, in recent years the trend has been toward smaller-sized CCDs. However, if the optimum optic-axial distance is determined such that a part of the object optical system nearest to the object has a moderate parallax, and an image is formed on the CCD with that optic-axial distance, as shown in FIG. 8, the center of an image will be positioned at the end of the CCD, if the CCD is small. That is, the area of the images at the right and left sides of the CCD, marked with diagonal lines in FIG. 8, decreases and causes interference with the stereoscopic vision and measurements.
Conversely, if the size of the CCD to be used and the optimum distance between the centers of the images on the CCD is also determined in accordance with the size of an endoscope, as shown in FIG. 9, there is a possibility that a parallax required for a measurement or for stereoscopic vision cannot be obtained if the optic-axial distance for the object optical system on the object side (nearest the object) is equal to the distance between the centers of the images on the CCD.
Therefore, in order to obtain a moderate parallax required for a measurement or a stereoscopic vision as well as an acceptable image on the CCD, the optic-axial distance of an object optical system, and the distance between the centers of the images on CCD need to be varied.
However, the optic-axial distance of an object optical system influences a parallax which is important at the time of a stereoscopic-vision observation and the precision at the time of measurement. If the optic-axial distance of the object optical system nearest to the object is narrow, a parallax will decrease so that depth information becomes hard to obtain when carrying out a stereoscopic vision and a measurement error becomes large when carrying out a measurement operation.
Conversely, if the optic-axial distance of the object optical system nearest to the object is wide, a parallax will become large. Although the precision of a measurement improves, the problem will arise that the end of an endoscope becomes large. And since a parallax is too large when carrying out a stereoscopic-vision observation, it is hard to observe on the contrary.
A parallax depends not only on the optic-axial distance of the object optical system nearest to the object but also on the distance to the object to be observed. In other words, the closer the object is, the larger the parallax becomes, and the farther it is, the smaller the parallax becomes.
Based on the above, in order to obtain a moderate parallax required for measurement and for a stereoscopic-vision observation depending on the observation distance, and in order not to make the size of an endoscope large, the optic-axial distance of the object optical system at a part thereof nearest to the object should be determined.
A conventional example in which the optic-axial distance of an object optical system is different from the distance between the centers of the images on the CCD is described in the Japanese Laid-open Patent Publication No. 62-215221.
In this example, as shown in FIG. 10, by sandwiching a parallel flat refractive element with a pair of optical systems, the optic-axial distance of an object optical system is narrowed towards the center of the image on the CCD. In such an optical system, if the CCD is small, the parallel flat dioptric element must be small. However, it is difficult to design and manufacture a small parallel flat dioptric element, and still more difficult to sandwich it with a pair of optical systems.
It is an object of the present invention to provide an object optical system with a moderate parallax and a moderate image size, without making the insertion part of the endoscope thick in diameter.
In an endoscope apparatus, according to the present invention, equipped with an object optical system to conduct a measurement or a stereoscopic-vision observation, as shown in FIG. 1, the object optical system comprises a pair of negative lenses; a first pair of positive-lenses; a brightness diaphragm; a second pair of positive-lenses; and an image-pick-up device for forming an object image. These elements are arranged in order from an object side. A pair of optical axes are defined by the pair of negative lenses, the first pair of positive-lenses and the brightness diaphragm. The second pair of positive-lenses are arranged eccentrically with respect to the pair of optical axes in a direction towards each other.
Each lens of the second pair of positive-lenses can be defined as a single-lens, plural single-lenses, or cemented lens or combination thereof.
The eccentric lenses may be provided on only one side of the second pair of positive-lenses, or on a part of the second pair of positive-lenses. It is noted that the centers, of the positive-lenses of the second pair, is the center of the circle if the lens shape is a circle, and it is the center of gravity of a polygon if the lens shape is a polygon.
The endoscope apparatus according to this invention, wherein the following conditional expression is satisfied:
0.2xe2x89xa6x/dxe2x89xa60.9xe2x80x83xe2x80x83(1)
wherein x represents an optic-axial distance of said pair of optical axes on the image-pick-up device side, and d represents the optic-axial distance of said pair of optical axes of the object side, the brightness diaphragm, respectively.
The positive-lenses of the second pair are arranged eccentrically with respect to a pair of optical axes in a direction in which the lenses come closer to each other symmetrically and by the same amount. According to this invention, the second pair of positive-lenses on the image-pick-up device side from a brightness diaphragm is arranged to be inwardly eccentric, with respect to each optical axis on the object side from a brightness diaphragm, towards the horizontal direction of the CCD surface.
The amount of the eccentricity of the second pair of positive-lenses does not necessarily need to be symmetrical. In a stereoscopic-vision endoscope, however, it is important to minimize the aberrational difference of the left and right images. It is preferable that the left and right images are balanced by making the eccentricity symmetric.
Moreover, each of the positive-lenses of the second pair has a cutout portion at the peripheral thereof where the two lenses abut so that the centers of the positive-lenses come closer to each other. Specifically, the distance between the centers of circumferences of the positive-lenses is less than the sum of radii thereof. It is preferable that the shape of the cutout portion be a straight line which is easy to process.
The positive-lenses of the second pair are arranged to tile eccentrically by angle a, as shown in FIG. 4, in a manner that each optical axis includes inwardly from the object side toward the image side symmetrically and by the same amount.
The amount of eccentricity of the second pair of positive-lenses does not necessarily need to be symmetrical. In a stereoscopic-vision endoscope, however, it is important to minimize the aberrational difference of the left and right images. It is preferable that the left and right images are balance by making the eccentricity symmetric.
Moreover, each of the positive-lenses of the second pair has a cutout portion at the peripheral thereof where the two lenses abut so that the centers of the positive-lenses come closer to each other. Specifically, the distance between the centers of circumferences of the positive-lenses is less than the sum of radii thereof. It is preferable that the shape of the cutout portion be a straight line which is easy to process.
According to this invention, it is constituted so that the following conditional-expression (2) may be satisfied:
0.03L less than d less than 2Lxe2x80x83xe2x80x83(2)
wherein d represents the optic-axial distance of said pair of optical axes at the object side, and L represents the best observation distance of said object optical system.
The minimum of this equation is necessary a condition in order to obtain a parallax and furthermore obtain precision required at the time of measurement. As illustrated in FIG. 1, when setting the best observation distance at L, it is considered that 1 degree more is required for an convergence angle (xcex8). The best observation distance herein implies a distance to the object which is most suitable for the observation. In the case of an endoscope, it is usually about 5-100 mm. If the convergence angle (xcex8) is 1 degree or less, a parallax will decrease and it becomes hard to obtain information on the depth direction when carrying out the stereoscopic vision. Moreover, in that case, a measurement error becomes large when measuring an objective shape.
The value of the upper limit of the above formula (2) not only restrains the size of an end portion of the endoscope from becoming large, but also prevents the observation from becoming difficult to observe because of a too large parallax.
According to this invention, the end adapter is detachable from the image-pick-up device.
As illustrated in FIG. 1, an end adapter system which includes the pair of negative lenses, the first pair of positive lenses, the brightness diaphragm and the second pair of positive lenses is detachable in the direction of an arrow at the chain-line position. The rear part is the endoscope side part containing a cover glass 7 and an image-pick-up device 8. Accordingly, the angle of view of the endoscope, the viewing angle, and the convergence angle which influences a parallax are arbitrarily exchangeable by replacing the adapter part.
According to this invention, a prism for covering the line of sight is arranged between an object and the pair of negative lenses, as shown in FIG. 3(b) (side view of FIG. 3(a)). As apparent from FIGS. 3(a) and 3(b), at least one prism for converting the line of sight 10, a pair of negative lenses 1, a first pair of positive-lenses 2, a brightness diaphragm 3, the second pair of positive-lenses 4, and an image-pick-up device 8 are provided in order from the object side. The second pair of positive-lenses are eccentric with respect to each of the optical axis on the object side from the brightness diaphragm. With this structure, the angle of view is determined by the pair of negative lenses and the first pair of positive-lenses on the object side from the brightness diaphragm. Simultaneously, aberrations, such as a spherical-aberration and curvature of field, are restrained as well. And, by shifting the optical axes of the second pair or positive lenses after reducing a diameter of a luminous flux through the brightness diaphragm, the aberrational influence by eccentricity is decreased. Free selection of the line of sight is effective is observing a narrow space.
According to an embodiment of this invention, an effective image-pick-up range of the image-pick-up device is 2 to 2.5 mm or less.
In the object optical system of the endoscope according to the present invention, as shown in FIG. 5, the object optical system comprises a brightness diaphragm 3, a pair of positive-lenses 11, 12 and an image-pick-up device 8 for forming an object image. These elements are arranged in order from the object side. An optic-axially eccentric device 13 is arranged adjacent the brightness diaphragm 3, and the optic-axial distance on the object side determined by the optic-axially eccentric device 13 is eccentric with respect to the optic-axial distance determined by a pair of positive-lenses 11, 12 on the image side from the brightness diaphragm.
Moreover, according to this invention, the following conditional-expression (1) is satisfied:
0.2xe2x89xa6x/dxe2x89xa60.9xe2x80x83xe2x80x83(1)
wherein x represents an optic-axial distance of a pair of optical axes on the side of the image-pick-up device from the brightness diaphragm, and d represents the optic-axial distance of the pair of optical axes on the side of an object from the brightness diaphragm.
The optic-axially eccentric device is disposed within 0.5 mm from the brightness diaphragm. The reason why the optic-axially eccentric device is provided adjacent to the brightness diaphragm is that the size of the optic-axially device becomes small if the amount of eccentricity becomes comparatively small when using a small-sized image pick-up device. Therefore, it is desirable to arrange it adjacent to the brightness diaphragm with a low light height.
The term xe2x80x9cadjacent the brightness diaphragmxe2x80x9d herein implies not only that the optic-axially eccentric device is disposed within 0.5 mm from the brightness diaphragm, but also that the brightness diaphragm can be disposed within the optic-axially eccentric device. In this embodiment, it is preferable that the small image-pick-up device have an effective image-pick-up range of 2 to 2.5 mm or less.
In this constitution, it is more desirable to provide the optic-axially eccentric device on one of the optical systems which shifts the optical axis in a horizontal direction of the CCD image surface. This is because, in the endoscope of a narrow diameter, if two optical elements which make the optical axes eccentric are used, like a prior art example, each optical element should be made small and a manufacture process becomes much more difficult.
According to another embodiment, the optic-axially eccentric device has a prism with two reflecting surfaces, or two reflective mirrors.
According to this invention, the following conditional expression is satisfied:
0.03L less than d less than 2Lxe2x80x83xe2x80x83(2)
wherein d represents the optic-axial distance of a pair of optical axes on the object side from said brightness diaphragm, and L represents the best observation distance of the object optical system.
Preferably, the end adapter is detachable from the image-pick-up device. Preferably, the effective image pick-up-range of the image pick-up-device is 2 to 2.5 mm or less.